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I'm trying to read the battery voltage using Arduino, using a 9V battery. I keep getting the same voltage (4.99). I connected my Arduino to Matlab so I'm only using the command voltage=readVoltage(a,'pin'). I'm very new to this, so any help would be appreciated.

thats my circuit

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Analog inputs on the arduino will measure 5v maximum. If you want to mesure higher voltage you will have to use a voltage divisor circuit (resistors).

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    Also your analog input might now be dead from providing almost twice the voltage it's designed for. – Majenko May 2 '17 at 9:42
  • Aren't you getting any Magic smoke ? – Sagnik Pradhan May 2 '17 at 13:02
  • Thank you all, somehow I didnt damage the analog input, thank God. But i tried with resistors (10k) and its still measuring the same voltage... – Soundouss Sassi May 2 '17 at 17:20
  • And if you measure with a multi-meter the voltage at the Arduino input ? – Andre Courchesne May 2 '17 at 17:21
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    @SoundoussSassi could you show/describe how you have connected the resistors (just to make sure it is a proper voltage divider)? I also wonder if it is necessary to select a proper reference (there should be an internal and external reference possible). – Ghanima May 2 '17 at 18:53

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